High-tin titanium welding wire



United States Patent 3,340,028 HIGH-TIN TITANIUM WELDING WIRE Milton B.Vordahl, Las Vegas, Nev., assignor to Crucible Steel Company of America,Pittsburgh, Pa., a corporation of New Jersey No Drawing. Originalapplication July 17, 1964, Ser. No. 383,487, now Patent No. 3,302,282,dated Feb. 7, 1967. Divided and this application Nov. 30, 1966, Ser. No.597,846

3 Claims. (Cl. 29-198) ABSTRACT OF THE DISCLOSURE This invention relatesto Weldments of titanium and base alloys thereof, and in particular toweldments made with the use of a high-tin titanium-base alloy. Inaddition this invention relates to welding wire made of a high-tintitanium-base alloy for use in making such weldments. More specifically,the invention contemplates the use of a titanium-base alloy containingtin in an amount up to about 20% by weight and preferably within therange 13 to 18% by weight with the optimum tin content being about 15%by weight. Tin is used because of its characteristic as a potentinhibitor of beta decomposition and because it is widely soluble in bothalpha and beta titanium. Consequently, in welding applications, it actsto prevent embrittlement ordinarily caused by beta decomposition.

This application is a division of my earlier-filed copending applicationSer. No. 383,487, filed July 17, 1964, now Patent No. 3,302,282, whichis in turn a continuation-in-part of my earlier-filed copend-ingapplication Ser. No. 130,494, filed Aug. 10, 1961, now abandoned.

In the process of fabricating metal structures by joining standardshapes, welding is probably the most widely used of the joiningoperations. In the case of fusion welding, the more common methods ofWelding, weld or filler metal is often employed, and the base metal,i.e., the metal being welded, is heated to temperature-s well above itsmelting point and is invariably melted in the immediate vicinityof thejoint. As a result of the temperatures attained in the base metal,important changes may .occur therein. In this regard, cooling rate andmaximum temperature are of extreme importance, especially in connectionwith titanium, titanium-base alloys, and other metals undergoingtransformation of phases. For example, where a base metal has beenintentionally hardened by cold working prior to welding, an undesirableloss in strength may be occasioned should the work be heated above acritical temperature range. The detriment is most pronounced in thoseportions of the base metal adjacent to the joint, since such portionsare more prone to be heated to the critical temperature range andthereby undergo recrystallization. Where the heat is sufficientlyintense to raise the temperature above this range, grain growth occurs.The cooling rate, of course, is significant in the obtention of a stableand ductile weld and is dependent upon the composition of the weldmetal.

Since the ability to make a ductile fusion joint of a given metal isoften of significant or even of controlling importance in determiningthe usefulness of the metal, it follows that in such cases as titaniumand titanium-base alloys, where hot-strength properties are outstandingfor such vital applications as missiles and aircraft, the hotstrengthproperties will be of little consequence in many cases unless ductilewelds are obtainable.

In the consideration of the weldability of titanium and titanium-basealloys, a discussion of crystal mechanics is in order, and in thisconnection the common crystallographic classification may be employed,i.e., alpha, beta,

3,340,028 Patented Sept. 5, 1967 and combined alpha-beta. Fundamentally,titanium undergoes a crystallographic transformation from hexagonalalpha to body-centered beta at about 1625 F., and increasing amounts ofmany of its common alloying elements progressively drop the lowesttemperature at which the crystal structure is entirely body-centereduntil, finally, it possesses that structure at well below roomtemperature. Of the crystallographic types, alpha alloys, includingcommercial titanium, exhibit relatively poor bend ductility and a weldductility which is comparable to that of the alpha base metal, whilebeta alloys (heattreatable and not heat-treatable) exhibit relativelyhigh bend ductility and excellent weld ductility. Combined alpha-betaalloys exhibit a compromise performance reflecting, roughly, theproportions of alpha and beta pres ent, i.e,, the more beta present, thebetter the bend performance. Unfortunately, combined alpha-beta alloyshave a weld ductility even poorer than that of alpha alloys.

In addition to the crystal mechanics heretofore discussed, it isimportant to note the effect of specific alloying elements. Alphastabilizers promote or stabilize the alpha form over a wider temperaturerange, i.e., they raise the transformation temperature range, whereasbeta stabilizers stabilize the beta form over a wider temperature range,i.e., they lower the transformation temperature range. Where very largeadditions of beta stabilizers are made to titanium, a completely stablebeta alloy results, i.e., an alloy having an entirely beta crystalstructure which will not transform, regardless of thermal and mechanicaltreatment, between room temperature and the melting point. Between thevery large beta-stabilizing additions of the stable beta and the mediumadditions of the combined alpha-beta alloys is a region in which thealloys quite readily retain the beta structure in an unstable form, evenon air cooling. Thus, beta alloys can be classified as eitherheat-treatable (unstable) or nonheat-treatable (stable). With unstablebeta alloys, aging for several hours to several days at temperatures inthe range of 300 to 800 F. permits some unstable beta to transform, andthis transformation is often accompanied by embrittlement. Thisembrittlement, with some uncertainty, has been attributed to theformation of a transitory omega phase. Overaging, however, results indisappearance of the omega phase and obtention of a structure exhibitingmaximum ductility and stability and containing stable beta and alpha.

From the foregoing it would appear that weld ductility of combinedalpha-beta alloys would be impaired by the addition of alphastabilizers, since said alloys would tend to behave more like all-alphaalloys, i.e., exhibit relatively poor weld ductility. It would alsoappear that the addition to such alpha-beta alloys of beta stabilizerswould in many cases result in embrittlement, since the tendency would beto retain the beta structure in an unstable form that would transformduring aging. That this is indeed the case is borne out by thelong-standing problems of avoiding embrittlement and obtaining usefulductility in titanium weldrnents.

Accordingly, it is a principal object of the present invention toprovide a method of welding for producing a weld which remainssubstantially free from embrittlement on aging.

Another object of the invention is to provide a method of welding forproducing a weld which can be overaged to useful ductility.

A further object of the invention is to provide a method of weldingtitanium and titanium-base alloys employing a tin-containingtitanium-base alloy weld metal for producing a Weld which is relativelyductile and tough and remains substantially free from embrittlement onaging.

Yet another object of the invention is to provide a weldment comprisingan assembly wherein component parts are joined with a tin-containingtitanium base alloy weld metal, the resultant weld being relativelyductile and tough and free from embrittlement on aging.

Other objects of the invention will be obvious from the followingdescription.

The present invention contemplates the use of a titanium-base alloycontaining tin, e.g., up to about 20% by weight, as a weld or fillermetal, particularly for use in the fusion welding of titanium andtitanium-base alloys. The amount of tin employed in the weld metalshould be at least effective to accomplish the desired results ofrendering the resultant weld relatively ductile and tough and free fromembrittlement on aging. The maximum tin employed is dictated byapproaching that value beyond which other physical properties aresignificantly impaired. A preferred range of about 13 to 18% tin byweight, and an optimum value of about 15% tin by weight was determined.The selection of tin as an alloying element was based on the findingthat tin is a potent inhibitor of beta decomposition and is widelysoluble in both alpha and beta titanium. Hence, no degree of dilutionwith the base produces an intrinsically brittle composition. The reasontherefor is that the effect of dilution by the titanium, i.e.,accelerated aging, is canceled out by the effect of dilution by the tin,i.e., retarded aging. Where there is dilution by the weld metal of abase metal containing a high proportion of beta phase, the sluggishnessconferred by the tin on the decomposition of beta slows aging of theresultant weld metal and avoids embrittlement by the base aging cycle.On the other hand, where there is dilution by the weld metal of a basemetal containing a low proportion of beta phase, the resultant weldmetal does not age to embrittlement by any cycle, i.e., aging effectsare not readily detectable or, alternatively, overaging to a usefulductility occurs.

In the course of the investigation leading to the instant invention,coupons of beta titanium (13% V, 11% Cr, 3% Al) were welded transverselywith a weld metal comprising a tin-containing titanium-base alloy (about14% Sn, balance Ti). The coupons were then aged (about 8 hours at 900F.) and tensile-tested. All coupons failed in the weld metal withexcellent ductility and exhibited an average tensile strength of about120,000 p.s.i., which value is high enough for broad usefulness.

It will be understood that the invention relates to a process of weldingwherein there may be applied to an assembly of pieces to be welded atleast one weld-effecting physical influence, i.e., heat or pressure.Alternatively, the high-tin welding wire may be first fused and thenapplied to the joint in the molten state.

Although the invention has been described in connection with a certainspecific embodiment, it will be readily apparent to those skilled in theart that various changes can be made to suit requirements withoutdeparting from the spirit and scope of the invention.

I claim:

1. A weldment comprising an assembly wherein component parts of atitanium-base alloy wherein at least a portion of the microstructurethereof is beta are joined with a weld metal consisting essentially of atin-containing titanium base alloy, the amount of tin ranging from anamount effective to produce a relatively ductile weld metal free fromembrittlement on aging to about 20% by weight.

2. A weldment as in claim 1 wherein the amount of tin is within therange of 13 to 18% by weight.

3. A weldment as in claim 1 wherein the amount of tin is about 15% byweight.

References Cited UNITED STATES PATENTS 2,669,514 2/1954 Finlay et al.l75.5 2,902,755 9/1959 Salt et al. 29504 X 2,906,008 9/1959 Boegehold etal. 29504 X FOREIGN PATENTS 785,293 10/1957 Great Britain.

OTHER REFERENCES Journal of Metals, January 1954, pages 25-29 relied on.

CHARLES N. LOVELL, Primary Examiner.

DAVID L. R-ECK, Examiner.

1. A WELDMENT COMPRISING AN ASSEMBLY WHEREIN COMPONENT PARTS OF ATITANIUM-BASE ALLOY WHEREIN AT LEAST A PORTION OF THE MICROSTRUCTURETHEREOF, IS BETA ARE JOINED WITH A WELD METAL CONSISTING ESSENTIALLY OFA TIN-CONTAINING TITANIUM BASE ALLOY, THE AMOUNT OF TIN RANGING FROM ANAMOUNT EFFECTIVE TO PRODUCE A RELATIVELY DUCTILE WELD METAL FREE FROMEMBRITTLEMENT ON AGING TO ABOUT 20% BY WEIGHT.